Balancing Redox Equations — Ion-electron method
Redox Reactions
5
JEE Qs
8%
Hard
60
min
Systematically follow the step-by-step procedure for each half-reaction, paying close attention to the reaction medium (acidic/basic) and ensuring both mass and charge are balanced at every stage, especially during electron addition and final combination.
🧮 Key Formulas
✅ Key Points for JEE
- 1Always separate the overall reaction into two half-reactions: one for oxidation and one for reduction.
- 2Balance all atoms other than oxygen and hydrogen first in each half-reaction.
- 3Carefully apply the correct rules for balancing oxygen and hydrogen based on whether the reaction occurs in acidic or basic medium.
- 4Balance the net charge in each half-reaction by adding electrons to the more positive side. Ensure the total number of electrons lost in oxidation equals the total number of electrons gained in reduction before combining half-reactions.
- 5Verify the final balanced equation by checking conservation of mass (all atoms) and conservation of charge on both sides.
⚠️ Common Mistakes
- ✕Incorrectly assigning oxidation numbers, leading to wrong identification of oxidation/reduction.
- ✕Confusing the rules for balancing H and O in acidic vs. basic medium (e.g., adding H+ in basic medium without subsequent OH- neutralization).
- ✕Errors in calculating the net charge of a half-reaction or adding the wrong number of electrons.
- ✕Failing to multiply half-reactions by appropriate integers to equalize the number of electrons before combining them.
- ✕Incorrectly cancelling common species (H+, OH-, H2O, e-) after combining the half-reactions.
📝 Practice Questions
See allQ63.Given below are two statements: Statement I: In the oxalic acid vs KMnO4 (in the presence of dil H2SO4 ) titration the solution needs to be heated initially to 60∘C, but no heating is required in Ferrous ammonium sulphate (FAS) vs KMnO4 titration (in the presence of dil H2SO4 ) Statement II: In oxalic acid vs KMnO4 titration, the initial formation of MnSO4 takes place at high temperature, which then acts as catalyst for further reaction. In the case of FAS vs KMnO4 , heating oxidizes Fe2+ into Fe3+ by oxygen of air and error may be introduced in the experiment. In the light of the above statements, choose the correct answer from the options given below (1) Both Statement I and Statement II are false (2) Both Statement I and Statement II are true (3) Statement I is false but Statement II is true (4) Statement I is true but Statement II is false 2025 (28 Jan Shift 1) JEE Main Previous Year Paper
Q69.Given below are two statements : Statement (I): In partition chromatography, stationary phase is thin film of liquid present in the inert support. Statement (II) : In paper chromatography, the material of paper acts as a stationary phase. In the light of the above statements, choose the correct answer from the options given below : (1) Statement I is true but Statement II is false (2) Statement I is false but Statement II is true (3) Both Statement I and Statement II are false (4) Both Statement I and Statement II are true
Q57.The species which does not undergo disproportionation reaction is : (1) ClO−3 (2) ClO− (3) ClO−2 (4) ClO−4
Q53.Which of the following oxidation reactions are carried out by both K2Cr2O7 and KMnO4 in acidic medium? A. Γ−→I2 B. S 2−→S C. Fe2+ →Fe3+ D. Γ−→IO3− E. S2O32−→SO42− Choose the correct answer from the options given below: (1) C, D and E Only (2) B, C and D Only (3) A, D and E Only (4) A, B and C Only
Q54.Only 2 mL of KMnO4 solution of unknown molarity is required to reach the end point of a titration of 20 mL of oxalic acid (2M) in acidic medium. The molarity of KMnO4 solution should be M.
Q58.The difference in the 'spin-only' magnetic moment values of KMnO4 and the manganese product formed during titration of KMnO4 against oxalic acid in acidic medium is _______ BM. (nearest integer)
NCERT Chapters
- Class 11 Chemistry Ch 8: Redox Reactions